Resistor type split phase motor



Dec. 10, 1940. Q BALLMAN 2,224,422

RESISTOR TYPE SPLIT PHASE MOTQR Filed June 9, 1957 Invenfor: Edwin C. Bal/man Affomeys Patented Dec. 10, 1940 UNITED STATES PATENT OFFICE 1 Claim.

This invention pertains to single phase alternating current motors of the resistor type. This is a split phase motor having main and starting windings in which the phase difference in the ourrent in these two windings is obtained by connecting a resistance in series With the starting winding.

According to present practice the split phase motor ofthe resistor type is provided with a main running winding and a starting winding Wound in a diiTerent magnetic axis from that of the main winding. The starting winding is Wound of high resistance wire of a small cross section in order that the comparatively short length of wire required for the starting winding may have sufficient resistance to provide the necessary phase difference. Such motors are subject to the Weakness that the small section wire of the starting winding is incapable of carrying the comparatively heavy starting current for any considerable length of time without overheating to a dangerous degree. For this reason this type of motor is ordinaril available only for starting a load which has low inertia so that it may be brought up to full speed in very short time.

One of the objects of this invention is to provide a motor of the split phase resistance type which is capable of starting a load having considerabIe inertia and requiring a considerable time to accelerate to full speed.

Another object is to provide such a motor with means for absorbing the heat which must be dissipated in the starting winding during such a long accelerating period so that both the motor and the resistor may not be over-heated.

Another object is to provide a resistor unit for such a motor of simple construction and such as to be able to absorb the heat dissipated therein during starting without undue rise of temperature.

Further objects will appear from the following description taken in connection with the accompanying drawing in which:

Figure 1 is a diagrammatic view of the stator circuit of a motor embodying this invention, and

Figure 2 is a vertical section of a resistor for such a motor constructed in accordance with this invention.

Referring to the drawing, l designates the main running winding of a split phase motor of the type here in question, and 2 represents the auxiliary or starting winding. A resistor indicated generally at 3 and provided with terminals 4 is connected in series with the starting winding 2. The circuit of the starting winding 2 is connected to the supply line through a switch 5 which may be operated centrifugally or otherwise to disconnect the starting winding when the motor has reached operating speed.

The starting winding 2, instead of being wound with comparatively high resistance wire in accordance with the practice heretofore, is wound with comparatively heavy copper wire, or other wire of low resistance. The cross sec- 10 tion of the wire on the winding 2 may be great enough so that this winding may carry the starting current for a period of two minutes or more without over-heating to a dangerous extent. The resistor 3 has sufiicient resistance to control 15 the current in the starting winding 2 and to produce the necessary phase difference between the current in that winding and that in the winding I.

Since all the resistance required for control of the starting current is in the resistor 3, all the energy dissipated in that resistor will be transformed into heat therein. If this resistor were constructed in the ordinary manner, that is by simply winding a spool of resistance wire it 5 would be subject to a dangerous rise of temperature. In accordance with the present invention however means are associated with said resistance to absorb the heat generated therein with a normal rise in temperature. By this ar- 30 rangement the temperature of the resistor 3 is kept low and accordingly said resistor may be mounted on or in the motor Without imposing upon the latter a dangerous temperature rise.

The structure of the resistor 3 is illustrated in 35 Figure 2. A metallic container 6 is provided within which the resistor element 1 is mounted. The container 6 is sealed by an insulating disc 8 which is seated upon a shoulder 9 formed in the container. The outer rim of the container is 40 spun over the edges of the disc 8 as indicated at Ill. The terminals 4 are mounted upon and pass through the disc 8 to the interior of the container where they are connected to the ends of the resistor element 1. A support II in the form 5 of a flat sheet of fiber or the like is seated at its upper edge in a groove in the lower face of the disc 8 and is provided at its lower edge with a notch l2 in which the middle portion of the resistor element 1 is seated. This element may be 50 constructed as a simple coil of wire in the ordinary manner and then stretched between the lower end of the support II and the terminals 4 as shown in the Figure 2. This forms a sufficiently rigid support for the element 1,

In order to absorb the heat generated in the element 1 during the starting of the motor the container 6 is filled with heat absorbing refractory material l3, preferably in granular form. Such materials as quartz, bauxite and the like are suitable for this purpose. This heat absorbing material is packed in the container 6 so as to fill the same and to closely surround the element 1 so to be capable of taking up the heat generated by that element. Such heat is therefore distributed through the mass of material l3 instead of being confined to the element 1 and accordingly a relatively large amount of heat may be absorbed with a comparatively slow temperature rise.

In the operation of this motor the same may be started under a heavy inertia load with the switch closed. Such a load will require considerable time in order to bring it up to full operating speed. During this time the heavy starting current is passing through the starting winding 2 and the resistor 3. However as the winding 2 has ample current capacity it will not be heated up to a dangerous extent. The heat generated in the starting circuit will be confined to the resistor 3. This heat is generated in the element land is transferred to the material l3 and is distributed throughout the mass of said material. When the motor has attained full speed the switch 5 is opened.

It will be seen that this invention provides means whereby a split phase motor of the resistor type is enabled to start a heavy inertia load requiring an extended starting period without danger of burning the starting winding 2. Furthermore, the arrangement is such that no portion of the equipment is subject to a dangerous temperature rise.

It is obvious that various changes inpthe details of construction, within the scope of the appended claim, may be made without departing from the spirit of the invention; it is understood, therefore, that the invention is not restricted to the specific details shown and described. 7

Having thus described the invention, What is claimed is:

The combination with a single phase motor of the character described having a starting winding of high current capacity such as to reduce the resistance of said Winding to an amount insufiicient to limit the current therein to the 'required starting value, of a resistor mounted on said motor, said resistor comprising a resistance element connected in series circuit relation with said starting winding and buried in a mass of refractory material having substantially high heatabsorbing properties.

EDWIN C. BALLMAN. 

